Antenna for magnetic resonance imaging and method of use

ABSTRACT

A medical appliance for use in magnetic resonance imaging procedures. A guidewire for vascular procedures is formed by a coaxial cable acting as antenna in a magnetic resonance imaging system.

CONTINUING DATA

This application is a continuation of application Ser. No. 08/311,700,filed 23 Sep., 1994, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a medical appliance for use in magneticresonance imaging procedures performed on a body, comprising an antennadetecting magnetic resonance response signals, the antenna intended tobe inserted into the body for interacting with a magnetic resonanceprocedure for calculating the position of the medical appliance in thebody.

Tracking of catheters and other devices positioned within a body may beachieved by means of a magnetic resonance imaging system in order toavoid using X-rays and the risk of accumulated X-ray dose to the patientand long term exposure to the attending medical staff.

Typically, such a magnetic resonance imaging system may be comprised ofmagnet means, pulsed magnetic field gradient generating means, atransmitter for electromagnetic waves in radio-frequency, aradio-frequency receiver, a processor, and a controller. The device tobe tracked has attached to its end a small coil of electricallyconductive wire. The patient is placed into the magnet means and thedevice is inserted into the patient. The magnetic resonance imagingsystem generates electromagnetic waves in radio-frequency and magneticfield gradient pulses that are transmitted into the patient and thatinduce a resonant response signal from selected nuclear spins within thepatient. This response signal induces current in the coil ofelectrically conductive wire attached to the device. The coil thusdetects the nuclear spins in the vicinity of the coil. Theradio-frequency receiver receives this detected response signal andprocesses it and then stores it with the controller. This is repeated inthree orthogonal directions. The gradients cause the frequency of thedetected signal to be directly proportional to the position of theradio-frequency coil along each applied gradient.

The position of the radio-frequency coil inside the patient maytherefore be calculated by processing the data using Fouriertransformations so that a positional picture of the coil is achieved.Since however the coil only reacts, literally not a positional pictureof the coil but in fact a positional picture of the position of theresponse signals inside the patient is achieved. Since this positionalpicture contains no information yet on the region surrounding theimmediate vicinity of the coil, this positional picture can besuperposed with a magnetic resonance image of the region of interest. Inthis case the picture of the region may have been taken and stored atthe same occasion as the positional picture or at any earlier occasion.

Radio-frequency antennas in the form of a coil couple inductively to theelectromagnetic field and they allow obtaining a substantially spatiallyuniform magnetic field which results in a relatively uniform imageintensity over a wide region. The problem is however that coilconfigurations are bulky (the received signal is determined by the loopdiameter) and cannot be implemented for use in narrow vessels, wherebytheir use for the placement of medical appliances such as catheters maybe critical.

Furthermore, the spot image which is provided for by the coil antennadoes not allow knowing or even evaluating the orientation of the device;as a result, the magnetic resonance imaging system cannot be used forsteering the device into tortuous areas such as blood vessels.

European Patent No 0165742 describes a catheter for use with magneticresonance imaging systems. This catheter comprises a sheath which hasembedded within the wall thereof a pair of conductors preferably formedof a foil composite obtained by plating of conductive materials ofselected magnetic susceptibility to yield a composite of desiredsusceptibility substantially matching that of the sheath. In this way,the magnetic invisibility of the catheter is maintained. The tip of thecatheter contains a loop connecting the conductors, the phase of such aloop being preferably transverse to the catheter symmetry axis. Asexplained in the document, when excited by a weak pulse source, the loopsupports a dipole magnetic field which locally distorts the magneticresonance image providing an image cursor on the magnetic resonanceimaging display, and a low magnetic susceptibility functional elementsuch as a light pipe threaded into the catheter sheath allows directionof the catheter through selected blood vessels. The essence of thisstructure is thus the accurate location and monitoring of the cathetertip.

However, this is achieved within the environment of a bulkyconfiguration which cannot be advanced through narrow vessels and whichcannot be steered by reference to the magnetic resonance imaging system.

The document WO 87/04080 shows surgical catheters composed ofalternating annular segments of non-magnetic materials which are highlyopaque to nuclear magnetic resonance examination and less opaque,respectively. These catheters have thin coatings of silicone rubber ontheir external surface as well as on internal surface of their maincentral lumen. A plurality of further lumens are distributedcircumferentially within the catheter wall and guidance wires are housedin said lumens, secured at the distal end of the catheter wall andcoupled to a joystick at the proximal end of the catheter for individualtightening and relaxing to permit radial guidance of the distal end ofthe catheter. The central lumen of the catheter and still furthersecondary lumens arranged in the catheter wall are for the distributionof various drugs or for surgical tools such as optic fiber for lasersurgery or suturing devices or still stitching grippers. By thesearrangements, location of the catheters is apparent under nuclearmagnetic resonance examination, visually at the distal end. Thesestructures are however bulky and they have the same drawbacks asoutlined hereinbefore.

European Patent Application published under N 0385367 shows aninsertable prostate pick-up probe devised for being a nuclear magneticresonance receiving device capable of imaging spectra from the humanprostate and surrounding tissue; this probe may also be used as thetransmit coil for radio-frequency excitation. This probe is intended tobe used with an interface network providing the tuning, impedancematching, and decoupling functions, and including a connection to amagnetic resonance imaging scanner.

The probe includes a shaft supporting a patient interface balloon at itsdistal end, comprising an inner balloon and an outer balloon, the innerballoon being capable of being inflated with air supplied through alumen within the shaft. A non-stretchable lane formed of an adhesivebacked cloth material partly covers the inner balloon and serves as aguide for a flexible receiving coil arranged between the inner balloonand the outer balloon, this coil being electrically connected to theinterface via an insulated cable extending through the shaft. Uponinflation, the non-stretchable plane rises and forces the receiving coiland outer balloon against the region of interest so that the receivingcoil is in position to receive the best possible radio-frequency signalfrom the region of interest. Special indentations forming a shell areprovided on the outer balloon to act as coil positioners when theballoon is in its uninflated state so that the coil may be repeatedlypositioned relative to the shell inside the outer balloon for numerousclinical inflation and deflation cycles. A colored stripe is marked onthe shaft, possibly including a scale, for indicating the distance whichthe shaft has been inserted into the patient and also the radialorientation of the balloon for proper alignment with the region ofinterest. In operation, the probe is inserted while the patientinterface balloon is in the uninflated state; the alignment stripemarked on the shaft is used to radially and longitudinally position theprobe within the region of interest. Once the probe is correctly placed,the patient interface balloon is inflated and the receiving coil isforced against the region of interest. The probe is then connected tothe interface network via the insulated cable.

This particular arrangement of the radio-frequency coil does not reducethe bulk of the system which cannot be used for narrow or tortuousvessels. Furthermore, the system does not provide for any information asto orientation of the probe for steering purposes.

The document DE-3937052 A1 shows a biopsy tube for use in a magneticresonance imaging procedure, comprising longitudinally extending coaxialconductor tubes separated by insulator tubes and extending the length ofthe biopsy tube. In a further embodiment, the conductor tubes arereplaced by gutter like portions of coaxial conductor tubes which areseparated by an insulator filling. Here again, the result is a bulkyconfiguration which cannot be advanced to narrow vessels. In addition,that kind of assembly is substantially stiff, thereby further preventingthe applicability of the instrument in tortuous vessels.

SUMMARY OF THE INVENTION

The object of this invention is to improve the possibilities of usingmagnetic resonance imaging procedures by means of a medical appliancewhich is simple and efficient, which may continuously provide a fullinformation as to its position and orientation, which occupies a minimalspace and which has a great flexibility so as to be capable of reachingnarrow and tortuous vascular configurations, which may be actuallysteered under magnetic resonance imaging, which may be used as aninterventional means, and which may also prove efficient in thedetermination of the vascular configurations.

To this effect, the medical appliance according to the inventioncomplies with the definitions given in the claims.

As opposed to the coil configuration, the open wire length antennacouples capacitively to the electromagnetic field and as the receivedsignal originates from the immediate neighborhood of the open wirelength, it becomes possible to obtain an image of the antenna, of itsposition, as well as of its orientation. Steering of the appliance isthus actually possible. The open wire length antenna may be extremelythin and it may also have a high flexibility, allowing safe driving andpassage through vascular configurations, even in tortuous and restrictedareas thereof. This opens way to using magnetic resonance imagingprocedures in interventional conditions where time and precision are ofthe essence. By repeatedly measuring, reconstructing, and displaying theimage with a very short image repetition time, a magnetic resonanceimaging fluoroscopy system can be created. And one could also use theopen wire length antenna to make a high resolution image of a vesselwall.

According to a simple inexpensive embodiment, the open wire lengthantenna may be formed by a coaxial cable.

According to an embodiment aiming very thin configurations, the openwire length antenna may be made of a coaxial cable in which the shieldand insulators are respectively made of a conductor coating andinsulating coatings. In both these cases, the first and secondconducting elements of the coaxial configuration may have the samelength or unlike lengths.

According to a further embodiment, also aiming very thin configurations,the open wire length antenna may be made of two conducting strandsinsulated from one another, twisted or parallel to one another. Andthese strands may have the same length or unlike lengths.

The open wire length antenna may be included in a catheter and the like.As opposed to coil antennas for which the received signal depends on theloop diameter, the diameter of the open wire length antenna is ofsecondary relevance and, therefore, the open wire length antenna may bedevised to form the whole or part of a guidewire as used in vascularprocedures for the positioning of catheters and the like.

DESCRIPTION OF THE DRAWINGS

These and other objects will become readily apparent from the followingdetailed description with reference to the accompanying drawings whichshow, diagrammatically and by way of example only, four embodiments ofthe invention.

FIG. 1 is a block diagram of a system environmental to the presentinvention.

FIG. 2 is a longitudinal part section of a first embodiment of theappliance according to the invention.

FIG. 3 is a longitudinal part section of a second embodiment of theappliance according to the invention.

FIGS. 4 and 5 ate longitudinal views of two further embodiments of theappliance according to the invention.

DETAILED DESCRIPTION

The system shown in FIG. 1 is a magnetic resonance imaging apparatus 1comprising a magnet system 2 for generating a homogeneous magnetic fieldon a subject 3 placed on a support table 4. Inside the magnet system 2is a coil structure 5 to produce around the subject a magnetic fieldobtained from radio-frequency energy source 6. Receiver 7 responds tothe resonance signal and processor 8 reconstitutes the integers of theprojection which will be shown on display 11. The medical appliance 9,inserted into subject 3, is connected via conductor 10 to controlstation 12. Such a general configuration is familiar to those skilled inthe art and it will not be described in further detail.

The appliance 9, as exemplified in FIG. 2, is a guidewire including anopen wire length antenna formed by a coaxial cable comprising a centralconductor 13 enclosed in an insulator 14 surrounded by a shield 15encased in an insulator 16. As used in this application, an open wirelength includes an open-ended or un-delimited piece of wire, as opposedto a closed wire length such as a piece of wire with a coilconfiguration at the end. The shield 15 and the outer insulator 16 ofthe coaxial cable have been removed from a portion distal end 17. Theproximal end (not shown) of the coaxial cable is for connection to thestandard antenna input of control station 12 as generally shown in FIG.1.

The appliance 9 of FIG. 3 is also a guidewire including an open wirelength antenna formed by a coaxial cable.

However, the insulator 140 14 surrounding the central conductor 130 isreplaced by an insulating coating 140, while the shield 15 is replacedby a conductor coating 150 and the insulator 16 by an insulator coating160. As for the embodiment of FIG. 3, the conductor coating 150 andinsulator coating 160 have been removed from a portion of the distal endof tip 170. Also, the proximal end (not shown) of this coaxial cable isadapted to connection to the standard antenna input of control station12 (FIG. 1).

Variants may be envisaged.

For instance, the outer conductor and insulator, 15-16 resp. 150-160,need not be removed from a portion of the distal end 17 resp. 170.Similarly, the outer conductor and insulator may be removed a fargreater length from the distal end 17 resp. 170, and it is also possibleto have them removed to the proximal end of the guidewire, outside ofthe patient.

Subject to the precautions or requirements inherent to patientprotection, it would be also possible to have the guidewire comprised ofa naked conductor 13 or 130, while the insulator 14 or 140 and outerconductor 15, 150 and insulator 16, 160 would be installed towards theproximal end of the guidewire, outside of the patient.

Similarly, the coaxial configuration shown is not compulsory, beingpossible to have the open wire length antenna as a naked or insulatedwire with appropriate polarities arranged for connection thereof to theantenna input of the control station.

FIG. 4 shows one such possibility, in which the open wire length antennais made of two twisted conducting strands 18 and 19 insulated from oneanother by appropriate coatings 20 and 21.

FIG. 5 also shows one such possibility, in which the open wire lengthantenna is made of two conducting strands 22 and 23 parallel to oneanother and separated by insulator coatings 24 and 25.

As for the previous embodiments, the strands 18 and 19, respectively 22and 23, may have the same length or unlike lengths.

In both the embodiments of FIG. 4 and FIG. 5, the channels 30 which areleft open along the insulated strands may be used for furtherinvestigation purposes when the open wire length antenna is placed inthe lumen of a catheter, for example for pressure readings.

1. A medical appliance comprising an elongated signal-receiving antennafor detecting and providing magnetic resonance response signals, theantennas adapted to be inserted into the body during magnetic resonanceimaging procedures and for providing the response signals used forcalculating a position of the medical appliance in the body, wherein theantenna comprises an open wire length including first and secondconductor means having proximal ends adapted and arranged forinterconnection to a receiver to couple the detected resonance responsesignals to the receiver, spaced-part distal ends, and at least a firstinsulator means for physically separating and electrically insulatingadjacent portions of the first and second conductor means, the distalends of the first and second conductor means and the at least firstinsulator means adapted and arranged for exposure to a field ofelectromagnetic energy during a magnetic resonance procedure to coupleelectromagnetic energy from the field into the antenna and detect andprovide the magnetic resonance response signals to the proximal ends ofthe conductor means.
 2. A medical appliance according to claim 1,wherein the open wire length antenna is formed of a coaxial cableincluding the first and second conductors in a coaxial arrangement.
 3. Amedical appliance according to claim 1, wherein the open wire lengthantenna is formed of a cable having the first conductor enclosed in thefirst insulator, the first insulator surrounded by the second conductorand the second conductor encased in a second insulator, and wherein saidfirst conductor and second conductor have the same length.
 4. A medicalappliance according to claim 1, wherein the open wire length antenna isformed of a cable having the first conductor enclosed in the firstinsulator, the first insulator surrounded by the second conductor, andthe second conductor encased in a second insulator, and wherein saidfirst conductor and second conductor have unlike lengths.
 5. A medicalappliance according to claim 1, wherein the open wire length antenna ismade of the first conductor, the first insulator includes a firstinsulating coating applied on said first conductor, the second conductorincludes a conducting coating surrounding said first insulating coating,and the antenna further includes a second insulating coating applied onsaid conducting coating, and wherein said first conductor and conductingcoating have the same length.
 6. A medical appliance according to claim1, wherein the open wire length antenna is made of the first conductor,the first insulator includes a first insulating coating applied on saidfirst conductor, the second conductor includes a conducting coatingsurrounding said first insulating coating, and the antenna furtherincludes a second insulating coating applied on said conducting coating,and wherein said first conductor and conducting coating have unlikelengths.
 7. A medical appliance according to claim 1, wherein the firstand second conductors of the open wire length antenna include conductingstrands insulated from one another.
 8. A medical appliance according toclaim 7, wherein the first and second conductor means are parallel toone another.
 9. A medical appliance according to claim 7, wherein thefirst and second conductor means are twisted.
 10. A medical applianceaccording to claim 7, wherein the first and second conductor means havethe same length.
 11. A medical appliance according to claim 7, whereinthe first and second conductor means have unlike lengths.
 12. A medicalappliance according to claim 1, wherein the open wire length antennaforms at least a part of a guidewire for vascular procedures.
 13. Amedical appliance antenna system for use in connection with magneticresonance imaging procedures, including: a medical appliance comprisingan elongated signal-receiving antenna for detecting and providingmagnetic resonance response signals, the antenna adapted to be insertedinto the body during magnetic resonance imaging procedures and forproviding the response signals used for calculating a position of themedical appliance in the body, wherein the antenna includes an open wirelength including first and second conductors having proximal endsadapted and arranged for interconnection to a receiver to couple thedetected response signals to the receiver, spaced-apart distal ends, andat least a first insulator for physically separating and electricallyinsulating adjacent portions of the first and second conductors, thedistal ends of the first and second conductors and the at least firstinsulator adapted and arranged for exposure to a field ofelectromagnetic energy during a magnetic resonance procedure to couplethe electromagnetic energy from the field to the antenna and detect andprovide the magnetic resonance response signals to the proximal ends ofthe conductors; and a receiver electrically connected to the antenna forreceiving the magnetic resonance response signals and providinginformation representative of the position of the medical appliance. 14.A medical appliance according to claim 13, wherein the open wire lengthantenna is formed of a coaxial cable including the first and secondconductors in a coaxial arrangement.
 15. A medical appliance accordingto claim 13, wherein the open wire length antenna is formed of a cablehaving the first conductor enclosed in the first insulator, the firstinsulator surrounded by the second conductor and the second conductorencased in a second insulator, and wherein said first conductor andsecond conductor have the same length.
 16. A medical appliance accordingto claim 13, wherein the open wire length antenna is formed of a cablehaving the first conductor enclosed in the first insulator, the firstinsulator surrounded by the second conductor, and the second conductorencased in a second insulator, and wherein said first conductor andsecond conductor have unlike lengths.
 17. A medical appliance accordingto claim 13, wherein the open wire length antenna is made of the firstconductor, the first insulator includes a first insulating coatingapplied on said first conductor, the second conductor includes aconducting coating surrounding said first insulating coating, and theantenna further includes a second insulating coating applied on saidconducting coating, and wherein said first conductor and conductingcoating have the same length.
 18. A medical appliance according to claim13, wherein the open wire length antenna is made of the first conductor,the first insulator includes a first insulating coating applied on saidfirst conductor, the second conductor includes a conducting coatingsurrounding said first insulating coating, and the antenna furtherincludes a second insulating coating applied on said conducting coating,and wherein said first conductor and conducting coating have unlikelengths.
 19. A medical appliance according to claim 13, wherein thefirst and second conductors of the open wire length antenna includeconducting strands insulated from one another.
 20. A medical appliancecomprising an elongated and signal-receiving antenna for detecting andproviding magnetic resonance response signals, the antenna adapted to beinserted into the body during magnetic resonance imaging procedures andfor providing the response signals used for calculating a position ofthe medical appliance in the body, wherein the antenna comprises an openwire length including first and second conductors having proximal endsadapted and arranged for interconnection to a receiver to couple thedetected resonance response signals to the receiver, spaced-apart distalends, and at least a first insulator for physically separating andelectrically insulating adjacent portions of the first and secondconductors, the distal ends of the first and second conductors and theat least first insulator adapted and arranged for exposure to a field ofelectromagnetic energy during a magnetic resonance procedure to coupleelectromagnetic energy from the field into the antenna and detect andprovide the magnetic resonance response signals to the distal ends ofthe conductors.
 21. A medical appliance according to claim 20, whereinthe open wire length antenna is formed of a coaxial cable including thefirst and second conductors in a coaxial arrangement.
 22. A medicalappliance according to claim 20, wherein the open wire length antenna isformed of a cable having the first conductor enclosed in the firstinsulator, the first insulator surrounded by the second conductor andthe second conductor encased in a second insulator, and wherein saidfirst conductor and second conductor have the same length.
 23. A medicalappliance according to claim 20, wherein the open wire length antenna isformed of a cable having the first conductor enclosed in the firstinsulator, the first insulator surrounded by the second conductor, andthe second conductor encased in a second insulator, and wherein saidfirst conductor and second conductor have unlike lengths.
 24. A medicalappliance according to claim 20, wherein the open wire length antenna ismade of the first conductor, the first insulator includes a firstinsulating coating applied on said first conductor, the second conductorincludes a conducting coating surrounding said first insulating coating,and the antenna further includes a second insulating coating applied onsaid conducting coating, and wherein said first conductor and conductingcoating have the same length.
 25. A medical appliance according to claim20, wherein the open wire length antenna is made of the first conductor,the first insulator includes a first insulating coating applied on saidfirst conductor, the second conductor includes a conducting coatingsurrounding said first insulating coating, and the antenna furtherincludes a second insulating coating applied on said conducting coating,and wherein said first conductor and conducting coating have unlikelengths.
 26. A medical appliance according to claim 20, wherein thefirst and second conductors of the open wire length antenna includeconducting strands insulated from one another.
 27. A medical applianceaccording to claim 20 and further including a receiver electricallyconnected to the antenna for receiving the magnetic resonance responsesignals and providing information representative of the position andorientation of the medical appliance.
 28. A medical apparatus forimaging a wall of a body cavity in a patient by interacting with amagnetic resonance imaging (MRI) system which generates a magnetic fieldgradient and electromagnetic (EM) radiation externally from the patientand transmits the gradient and EM radiation into the patient andreceives a response signal indicative of a resonant response from thepatient, the apparatus comprising: an open wire length antenna includingan open conductor length configured to be inserted into the cavity andprovide the response signal, based on the resonant response from aregion of the patient closely proximate the antenna, to the MRI system,where the open conductor length includes at least one open endedconductive element; and a controller coupled to the antenna andconfigured to receive the response signal to obtain an image of thecavity wall proximate the antenna.
 29. The medical apparatus of claim 28wherein the controller is configured to calculate antenna location byprocessing data to obtain an image of the antenna, antenna position, andantenna orientation.
 30. The medical apparatus of claim 28 wherein thecontroller is configured to repeatedly measure, reconstruct and storethe image to obtain an increased resolution image of the cavity wall.31. The medical apparatus of claim 28 wherein the antenna is configuredto be capacitively coupled to an EM field generated by the EM radiation.32. The medical apparatus of claim 28 wherein the cavity is defined byvasculature in the patient and wherein the antenna is configured forinsertion into and passage through the vasculature.
 33. The medicalapparatus of claim 32 wherein the antenna forms at least a portion of aguidewire configured for insertion into the vasculature for use inpositioning of a catheter.
 34. The medical apparatus of claim 28 whereinthe MRI system includes a response signal receiver and processor and acontrol station, and wherein the controller is implemented as a part ofthe control station or processor.
 35. The medical apparatus of claim 28wherein the antenna includes a first elongate conductor having a portionthereof forming the open conductor length, and a second elongateconductor, the first and second elongate conductors extending to aproximal end of the antenna.
 36. The medical apparatus of claim 35wherein the first and second elongate conductors are coaxially arrangedalong at least a portion of a length thereof.
 37. The medical apparatusof claim 35 wherein the first and second elongate conductors areseparated by an insulative layer.
 38. The medical apparatus of claim 35wherein the first and second elongate conductors are formed as a twistedpair.
 39. The medical apparatus of claim 35 wherein the first and secondelongate conductors are generally linear and generally parallel to oneanother.
 40. A method of generating an image of a wall of a body cavityin a patient, the method comprising: inserting an open wire lengthantenna including an open conductor length into the cavity, where theopen conductor length includes at least one open ended conductiveelement; generating a magnetic field gradient and electromagnetic (EM)radiation external from the patient and transmitting the gradient and EMradiation into the patient; transmitting a response signal, based on adetected resonant response from a region of the patient closelyproximate the antenna, to a magnetic resonance imaging (MRI) processor;receiving the response signal at the MRI processor; and obtaining animage of the cavity wall proximate the antenna based on the responsesignal.
 41. The method of claim 40 wherein obtaining an image comprises:repeatedly calculating antenna location.
 42. The method of claim 41wherein calculating antenna location comprises: processing data toobtain an image of the antenna.
 43. The method of claim 41 whereincalculating antenna location comprises: calculating antenna position.44. The method of claim 41 wherein calculating antenna locationcomprises: calculating antenna orientation.
 45. The method of claim 40wherein obtaining an image comprises: repeatedly measuring,reconstructing and storing the image to obtain an increased resolutionimage of the cavity wall.
 46. The method of claim 40 whereintransmitting a response signal comprises: capacitively coupling theantenna to an EM field generated by the EM radiation to detect theresonant response.
 47. The method of claim 40 wherein the cavity isdefined by vasculature in the patient and wherein inserting an antennainto the cavity comprises: inserting the antenna into the vasculature;and passing the antenna through the vasculature to a site to be imaged.48. The method of claim 47 wherein the antenna is configured as aguidewire and further comprising: positioning a catheter in thevasculature through use of the guidewire.
 49. A method of generating animage of a blood vessel wall of a blood vessel in a patient, the methodcomprising: inserting an open wire length antenna including an openconductor length into the blood vessel, where the open conductor lengthincludes at least one open ended conductive element; passing the antennathrough the blood vessel to a site to be imaged; generating a magneticfield gradient and electromagnetic (EM) radiation external from thepatient and transmitting the gradient and EM radiation into the patient;transmitting a response signal, based on a detected resonant responsefrom a region of the patient closely proximate the antenna, to amagnetic resonance imaging (MRI) processor; receiving the responsesignal at the MRI processor; and obtaining an image of the blood vesselwall proximate the antenna based on the response signal.
 50. A medicalapparatus for imaging a blood vessel wall of a blood vessel in a patientby interacting with a magnetic resonance imaging (MRI) system whichgenerates a magnetic field gradient and electromagnetic (EM) radiationexternal from the patient and transmits the gradient and EM radiationinto the patient and receives a response signal indicative of a resonantresponse from the patient, the apparatus comprising: an open wire lengthantenna configured to be inserted into the blood vessel and passed alongthe blood vessel to a site to be imaged and to provide the responsesignal, based on the resonant response from a region of the patientclosely proximate the antenna, to the MRI system, the antenna includingan open conductor length comprising at least one open ended conductiveelement; and a controller coupled to the antenna and configured toreceive the response signal and repeatedly calculate antenna location toobtain an image of the blood vessel wall proximate the antenna.
 51. Themedical apparatus of claim 50 wherein the antenna includes a firstelongate conductor having a portion thereof forming the open conductorlength, and a second elongate conductor, the first and second elongateconductors extending to a proximal end of the antenna.
 52. The medicalapparatus of claim 50 wherein the antenna is configured to becapacitively coupled to an EM field generated by the EM radiation.
 53. Amedical apparatus for imaging a body cavity wall of a body cavity in apatient by interacting with a magnetic resonanse imaging (MRI) systemwhich generates a magnetic field gradient and electromagnetic (EM)radiation external from the patient and transmits the gradient and EMradiation into the patient and receives a response signal indicative ofa resonant response from the patient, the apparatus comprising: an MRIopen wire length antenna configured to be inserted into the body cavityand passed along the body cavity to a site to be imaged and to providethe response signal, based on the resonant response from a region of thepatient closely proximate the antenna, to the MRI system, the antennaincluding an open conductor length comprising at least one open endedconductive element.
 54. The medical apparatus of claim 53 wherein thebody cavity is a blood vessel and further comprising: a controllercoupled to the antenna and configured to receive the response signal andrepeatedly calculate antenna location to obtain an image of the bloodvessel wall proximate the antenna.
 55. A method of generating an imageof a wall of a body cavity in a patient, the method comprising:inserting a magnetic resonance imaging (MRI) open wire length antennainto the body cavity, the antenna including an open conductor lengthcomprising at least one open ended conductive element; passing the MRIopen wire length antenna through the body cavity to a site to be imaged;and obtaining an MRI image of the body cavity wall proximate theantenna.
 56. The method of claim 55 wherein obtaining an imagecomprises: generating a magnetic field gradient and electromagnetic (EM)radiation external from the patient and transmitting the gradient and EMradiation into the patient; transmitting a response signal, based on adetected resonant response from a region of the patient closelyproximate the antenna, to an MRI processor; receiving the responsesignal at the MRI processor; and calculating antenna location based onthe response signal.
 57. The method of claim 56 wherein calculatingantenna location comprises: repeatedly calculating antenna location. 58.The method of claim 56 wherein transmitting a response signal comprises:capacitively coupling the antenna to an EM field generated by the EMradiation to detect the resonant response.
 59. The method of claim 55wherein obtaining an MRI image comprises: processing data to obtain animage of the antenna.
 60. The method of claim 55 wherein obtaining anMRI image comprises: calculating antenna position.
 61. The method ofclaim 55 wherein obtaining an MRI image comprises: calculating antennaorientation.
 62. The method of claim 55 wherein the body cavity is ablood vessel and obtaining an MRI image comprises: repeatedly measuring,reconstructing and storing the image to obtain an increased resolutionimage of the blood vessel wall.
 63. The method of claim 55 wherein thebody cavity is defined by vasculature and the antenna is configured as aguidewire and further comprising: positioning a catheter in thevasculature through use of the guidewire.
 64. A medical apparatus forimaging a wall of a body cavity in a patient by interacting with amagnetic resonance imaging (MRI) system which generates a magnetic fieldgradient and electromagnetic (EM) radiation and transmits the gradientand EM radiation into the patient and receives a response signalindicative of a resonant response from the patient, the apparatuscomprising: an antenna including an open conductor length configured tobe inserted into the cavity and provide the response signal, based onthe resonant response from a region of the patient closely proximate theantenna, to the MRI system wherein the antenna includes a first elongateconductor having a portion thereof forming the open conductor length,and a second elongate conductor, the first and second elongateconductors extending to a proximal end of the antenna; and a controllercoupled to the antenna and configured to receive the response signal toobtain an image of the cavity wall proximate the antenna.
 65. Themedical apparatus of claim 64 wherein the first and second elongateconductors are coaxially arranged along at least a portion of a lengththereof.
 66. The medical apparatus of claim 64 wherein the first andsecond elongate conductors are separated by an insulative layer.
 67. Themedical apparatus of claim 64 wherein the first and second elongateconductors are formed as a twisted pair.
 68. The medical apparatus ofclaim 64 wherein the first and second elongate conductors are generallylinear and generally parallel to one another.